--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/.gitignore	Fri May 15 10:12:16 2020 +0900
@@ -0,0 +1,27 @@
+syntax:glob
+
+# Created by https://www.gitignore.io/api/go
+# Edit at https://www.gitignore.io/?templates=go
+
+### Go ###
+# Binaries for programs and plugins
+*.exe
+*.exe~
+*.dll
+*.so
+*.dylib
+
+# Test binary, built with `go test -c`
+*.test
+
+# Output of the go coverage tool, specifically when used with LiteIDE
+*.out
+
+# Dependency directories (remove the comment below to include it)
+# vendor/
+
+### Go Patch ###
+/vendor/
+/Godeps/
+
+# End of https://www.gitignore.io/api/go

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/go.mod	Fri May 15 10:12:16 2020 +0900
@@ -0,0 +1,3 @@
+module firefly/hg/Members/anatofuz/monkey
+
+go 1.14

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/lexer/lexer.go	Fri May 15 10:12:16 2020 +0900
@@ -0,0 +1,109 @@
+package lexer
+
+import "firefly/hg/Members/anatofuz/monkey/token"
+
+// Lexer model
+type Lexer struct {
+	input        string
+	position     int // current position in input (points to current char)
+	readPosition int // current reading position in input(after current char)
+	ch           byte
+}
+
+// New create Lexer instance and start lex
+func New(input string) *Lexer {
+	l := &Lexer{input: input}
+	l.readChar()
+	return l
+}
+
+func (l *Lexer) readChar() {
+	if l.readPosition >= len(l.input) {
+		l.ch = 0
+	} else {
+		l.ch = l.input[l.readPosition]
+	}
+
+	l.position = l.readPosition
+	l.readPosition++
+}
+
+//NextToken is create token.Token after read from input
+func (l *Lexer) NextToken() token.Token {
+	var tok token.Token
+
+	l.skipWhitespace()
+
+	switch l.ch {
+	case '=':
+		tok = newToken(token.ASSIGN, l.ch)
+	case ';':
+		tok = newToken(token.SEMICOLON, l.ch)
+	case '(':
+		tok = newToken(token.LPAREN, l.ch)
+	case ')':
+		tok = newToken(token.RPAREN, l.ch)
+	case ',':
+		tok = newToken(token.COMMA, l.ch)
+	case '+':
+		tok = newToken(token.PLUS, l.ch)
+	case '{':
+		tok = newToken(token.LBRACE, l.ch)
+	case '}':
+		tok = newToken(token.RBRACE, l.ch)
+	case 0:
+		tok.Literal = ""
+		tok.Type = token.EOF
+
+	default:
+		if isLetter(l.ch) {
+			tok.Literal = l.readIdentifier()
+			tok.Type = token.LookupIdent(tok.Literal)
+			return tok
+		} else if isDigit(l.ch) {
+			tok.Type = token.INT
+			tok.Literal = l.readNumber()
+			return tok
+		} else {
+			tok = newToken(token.ILLEGAL, l.ch)
+		}
+
+	}
+
+	l.readChar()
+	return tok
+}
+
+func newToken(tokenType token.TokenType, ch byte) token.Token {
+	return token.Token{Type: tokenType, Literal: string(ch)}
+}
+
+func (l *Lexer) readIdentifier() string {
+	position := l.position
+	for isLetter(l.ch) {
+		l.readChar()
+	}
+	return l.input[position:l.position]
+}
+
+func isLetter(ch byte) bool {
+	return 'a' <= ch && ch <= 'z' || 'A' <= ch && ch <= 'Z' || ch == '_'
+}
+
+func (l *Lexer) skipWhitespace() {
+	for l.ch == ' ' || l.ch == '\t' || l.ch == '\n' || l.ch == '\r' {
+		l.readChar()
+	}
+}
+
+func (l *Lexer) readNumber() string {
+	positon := l.position
+	for isDigit(l.ch) {
+		l.readChar()
+	}
+	return l.input[positon:l.position]
+}
+
+func isDigit(ch byte) bool {
+	return '0' <= ch && ch <= '9'
+}

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/lexer/lexer_test.go	Fri May 15 10:12:16 2020 +0900
@@ -0,0 +1,57 @@
+package lexer
+
+import (
+	"firefly/hg/Members/anatofuz/monkey/token"
+	"testing"
+)
+
+func TestNextToken(t *testing.T) {
+	input := `let five = 5;
+	let ten = 10;
+
+	let add = fn(x, y) {
+		x + y;
+	}; 
+
+	let result = add(five, ten);
+	`
+
+	tests := []struct {
+		expectedType    token.TokenType
+		expectedLiteral string
+	}{
+		{token.LET, "let"},
+		{token.IDENT, "five"},
+		{token.ASSIGN, "="},
+		{token.INT, "5"},
+		{token.SEMICOLON, ";"},
+		{token.LET, "let"},
+		{token.IDENT, "ten"},
+		{token.ASSIGN, "="},
+		{token.INT, "10"},
+		{token.SEMICOLON, ";"},
+		{token.LET, "let"},
+		{token.IDENT, "add"},
+		{token.ASSIGN, "="},
+		{token.FUNCTION, "fn"},
+		{token.LPAREN, "("},
+		{token.IDENT, "x"},
+	}
+
+	l := New(input)
+
+	for i, tt := range tests {
+		tok := l.NextToken()
+
+		if tok.Type != tt.expectedType {
+			t.Fatalf("tests[%d] - tokentype wrong. expected=%q, got=%q",
+				i, tt.expectedType, tok.Type)
+		}
+
+		if tok.Literal != tt.expectedLiteral {
+			t.Fatalf("tests[%d] - literal wrong. expected=%q, got=%q",
+				i, tt.expectedLiteral, tok.Literal)
+
+		}
+	}
+}

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/token/token.go	Fri May 15 10:12:16 2020 +0900
@@ -0,0 +1,43 @@
+package token
+
+const (
+	ILLEGAL = "ILLEGAL"
+	EOF     = "EOF"
+
+	IDENT = "IDENT"
+	INT   = "INT"
+
+	ASSIGN = "="
+	PLUS   = "+"
+
+	COMMA     = ","
+	SEMICOLON = ";"
+
+	LPAREN = "("
+	RPAREN = "("
+	LBRACE = "{"
+	RBRACE = "}"
+
+	FUNCTION = "FUNCTION"
+	LET      = "LET"
+)
+
+type TokenType string
+
+type Token struct {
+	Type    TokenType
+	Literal string
+}
+
+var keywords = map[string]TokenType{
+	"fn":  FUNCTION,
+	"let": LET,
+}
+
+//LookupIdent is jugde ident or defined keywords
+func LookupIdent(ident string) TokenType {
+	if tok, ok := keywords[ident]; ok {
+		return tok
+	}
+	return IDENT
+}